The invention relates to spring contact probe needles for high frequency testing of integrated circuits and semiconductor wafers, and especially to providing accurate alignment and probe tip stability for spring probe needles, hereinafter referred to simply as probes, of the kind disclosed in FIGS. 2A-2G of commonly assigned patent xe2x80x9cPROBE ASSEMBLY AND METHOD FOR SWITCHABLE MULTI-DUT TESTING OF INTEGRATED CIRCUIT WAFERSxe2x80x9d, U.S. Pat. No. 5,923,178 issued Jul. 13, 1999 by Higgins et al., entirely incorporated herein by reference. This invention also relates to similar probe assemblies for providing high frequency test signal transmission between a printed circuit board of an integrated circuit xe2x80x9ctesterxe2x80x9d or xe2x80x9ctest systemxe2x80x9d and a probe card. The invention also relates to probe assemblies for providing high frequency test signal transmission between a printed circuit board of a test system and bonding pads of a large number of die of an integrated circuit wafer being tested.
U.S. Pat. No. 5,521,518 (Higgins), U.S. Pat. No. 5,589,781 (Higgins et al.), U.S. Pat. No. 5,416,429 (McQuade et al.), U.S. Pat. No. 4,554,506 (Faure et al.), U.S. Pat. No. 4,843,315 (Bayer et al.), U.S. Pat. No. 5,534,784 (Lum et al.) and U.S. Pat. No. 4,636,722 (Ardezzone) are generally indicative of the state of the art. It is known that insulative aluminum oxide is usually present on aluminum bonding pads of integrated circuit wafers. It also is known that there may be hundreds of integrated circuit die on a single semiconductor wafer and that it is necessary to xe2x80x9cprobe testxe2x80x9d each die or device under test (DUT) before the wafer is cut into individual integrated circuit die. The die testing often needs to be performed at high speed or high frequency, for example at a 100 MHz data rate, or even much higher.
The above references disclose various known techniques for supporting xe2x80x9cprobe cardsxe2x80x9d that support a plurality of probes, tips of which must provide reliable electrical contact (i.e., low probe contact resistance) with the bonding pads of the DUT during the testing. The shank of a probe is typically 5 to 10 mils in diameter. In a typical probe test system, a xe2x80x9ctest headxe2x80x9d supports an xe2x80x9cinterface assemblyxe2x80x9d, that is supported between a xe2x80x9cpin electronic boardxe2x80x9d of an integrated circuit test system and a xe2x80x9cprobe cardxe2x80x9d from which all of the probes required to probe test a particular semiconductor die extend. Typically, the wafer is supported on a xe2x80x9cwafer chuckxe2x80x9d of a xe2x80x9cwafer probe machinexe2x80x9d that automatically handles wafers. The chuck provides indexed translation in the x and y directions to bring the individual chip bonding pads into alignment with the probes supported by a probe card. The chuck ordinarily is moveable in the z (vertical) direction to press the chip bonding pads against the contact tips of the probe needles. After alignment of the probes with the corresponding bonding pads of the integrated circuit die, the wafer chuck and wafer thereon are raised approximately 3 mils so that the typically inclined probes xe2x80x9cscrubxe2x80x9d through brittle insulative aluminum oxide on the aluminum bonding pads of the wafer to allow good mechanical and electrical contact of the probe tip with the bonding pad metal and thereby ensure low probe contact resistance. It often would be desirable to perform the die testing at high frequencies, for example within a bandwidth of 2 to 6 Gigahertz or even much higher.
The C-shaped flex portions of the spring probes of the above referenced U.S. Pat. No. 5,923,178 have tips which extend beyond an insulative support. A problem of that structure is that the metal probe tips tend to be laterally skewed in various directions because of inaccuracies in the manufacturing process. This causes difficulty and inaccuracy in aligning the probe tips with the bonding pads of the integrated circuit under test. Another problem is that the probe tips have no lateral support in any direction, and therefore they tend to be somewhat unstable as they contact bonding pads as the wafer is raised so that its bonding pads are pressed against the spring probe tips.
Another problem with the structure of FIGS. 2A-2G of commonly assigned U.S. Pat. No. 5,923,178 is that the probe tips extend approximately 80-100 mils beyond the edge of the shank support structure and a ground plane associated with the shank support structure. This is a problem because although the portions of the probe needles supported on a thin insulator parallel to the ground plane act like a transmission line and provide very high bandwidth for test signals, the portions extending beyond the ground plane have appreciable inductance that significantly limits the bandwidth of probe test signals.
It would be beneficial to provide the numerous advantages of the xe2x80x9crocking tipxe2x80x9d of the arcuate spring needles described in the above referenced commonly assigned U.S. Pat. No. 5,923,178 without the above mentioned disadvantages of probe tip misalignment, instability, and probe tip inductance.
There are applications other than wafer probing for probe assemblies with probes of the kind described above. One such application includes providing high speed electrical signal coupling to conductors of a printed circuit board or between conductors of different printed circuit boards, wherein the probes electrically contact corresponding conductors on the surface or surfaces of one or more printed circuit boards.
A problem of prior art interface assemblies coupling a pin electronics board of a typical integrated circuit test system to a printed circuit board portion of a probe card is the very large force, often many hundreds of pounds, required to compress the spring-loaded pins so that their opposite contact tips reliably contact conductors of the pin electronics board and corresponding conductors of the probe card. Another problem with such prior interface assembles is the relatively low density of test signal paths that can be provided therein. The number of test signal paths is limited by the large pitch, approximately 100 mils, of the probe conductors contacting the pin electronics board. This is in sharp contrast to the pitch of approximately 20 mils of contact pads on the printed circuit board portion of a typical probe card, and is even sharper contrast to the approximately 5 mil pitch for bonding pads of some integrated circuits. At the present state of the art of integrated circuit test systems, it is not practical to simultaneously produce the test signals needed to probe test more than approximately 64 chips of a semiconductor wafer, each chip having roughly 60 bonding pads. Nor is it practical at the present state of the art to provide enough electric circuitry on each pin electronics board driven by the integrated circuit test system to test more than four chips or xe2x80x9csitesxe2x80x9d.
It would be desirable to provide an improved probe interface assembly for use between a xe2x80x9cpin electronics boardxe2x80x9d of a typical integrated circuit tester and a probe card. It also would be highly desirable to provide an improved assembly for conducting a much higher xe2x80x9cdensityxe2x80x9d of high frequency test signals, with bandwidth in excess of several gigahertz, directly between the pin electronics board of a typical integrated circuit tester and probe needles contacting the bonding pads of an integrated circuit wafer than has previously been achieved. It also would be highly desirable to provide simultaneous high speed, uniform impedance signal transmission directly between the pin electronics board of a typical integrated circuit tester and to bonding pads of a large number of die, e.g., 128 or more die, in an integrated circuit wafer being tested.
Accordingly, it an object of the invention to provide a probe card having a high density of flex probes and which avoids problems associated with uncontrolled impedance along the signal paths through the flex probes, and which also provides improved flex probe alignment and stability compared to the prior art.
It is another object of the invention to provide a high density of probe needles in an integrated circuit probe testing assembly (e.g., a probe card) which provides reliable electrical contact of probe tips to integrated circuit bonding pads without causing xe2x80x9cscrubbingxe2x80x9d, yet avoids problems associated with alignment, instability, and uncontrolled or non-uniform impedance associated with the curved flex probe structure described in the above referenced commonly assigned U.S. Pat. No. 5,923,178.
It is another object of the invention to provide a probe interface device including a high density of flex probes for coupling a large number of signals between corresponding conductors of separate printed circuit boards so as to provide improved alignment, stability and impedance properties.
It is another object of the invention to provide an improved interface device including a high density of flex probes for coupling a large number of test signals to/from corresponding conductors of at least one printed circuit board of a probe card assembly so as to provide improved alignment, stability and impedance properties compared to prior devices for coupling signals to/from conductors of a printed circuit board.
It is another object of the invention to provide an improved, controlled uniform impedance interface between the pin electronics board of an integrated circuit test system and a probe card.
It is another object of the invention to provide an interface assembly between a pin electronics board of an integrated circuit tester and a probe card, with a much higher density of test signal paths than has been achieved in the prior art.
It is another object of the invention to provide an interface assembly between a pin electronics board of an integrated circuit tester and a probe card which reduces the forces required to maintain reliable electrical contact between contact points of the interface system and corresponding conductors of the pin electronics board and the probe card.
It is another object of the invention to provide an interface assembly between a pin electronics board of an integrated circuit tester which allows parallel or simultaneous testing of as many as 128 or more integrated circuit die on a semiconductor wafer.
It is another object of the invention to provide high density, high speed, uniform, controlled impedance signal communication between a pin electronics board of an integrated circuit tester and bonding pads of an integrated circuit wafer being tested without use of a conventional probe card.
It is another object of the invention to provide high density, high speed, controlled impedance signal communication directly between a pin electronics board of an integrated circuit tester and bonding pads of an integrated circuit wafer being tested.
Briefly described, and in accordance with one embodiment thereof, the invention provides a probe assembly (14) including a plurality of probes (13 or 130) each having a shank portion (13A or 130A), a curved flex portion (13B or 130B) on a first end of the shank portion, and a contact tip on an end of the flex portion, thin dielectric material (16 or 180) of uniform thickness, each shank portion being supported in fixed parallel relation to a ground plane (25 or 132), each flex portion being moveable relative to the ground plane, at least part of each of the flex portions extending beyond an edge of the ground plane. In the described embodiments the dielectric material is smooth to allow guiding of the flex portions during flexing. The ground plane conductor and the dielectric material provide controlled, substantially uniform characteristic impedance and/or uniform signal transmission characteristics along the entire lengths of the probes.
Another embodiment of the invention provides an apparatus for high speed testing of an integrated circuit on a semiconductor wafer without substantial scrubbing so as to nevertheless achieve low probe needle contact resistance with low probe needle force, including a probe assembly (14) and a mechanical translating device 40. The probe assembly (14) includes a plurality of probe needles (13) each having a shank portion (13A), a curved flex portion (13B), and a contact tip (13C) on a free end of the flex portion, the shank portion (13A) being electrically coupled to an electrical test system, the shank portion (13A) of each probe being attached to a first surface (16A) of an insulative layer (16), a ground plane conductor (25) being attached to and supporting a second surface of the insulative layer (16). The flex portions (13B) of the probes (13) extend beyond an edge of the insulative layer (16). A portion (24) of the ground plane conductor (25) extends beyond the edge of the insulative layer (16) and is adjacent to all but an extending end (30) of the flex portion (13B) of each probe (13). A thin insulator/guide layer (26B) is attached to the extending portion (24) of the ground plane conductor (25) and is disposed between the extending portion (24) and the flex portions (13B) of the probes. The insulator/guide layer (26B) has a smooth, low friction surface to engage, guide, and stabilize the flex portions (13B) of the probes during flexing thereof, the insulative layer (16) and insulator/guide layer (269) providing matched impedance between the shank and flex portions of each of the probes. The mechanical translating device (40) operates to mechanically displace one of the semiconductor wafer (11) and probes (13) relative to the other to bring the contact tip (13C) of each probe into contact with a corresponding contact pad (12) of the semiconductor wafer (11) and to further mechanically displace one of the wafer and the probes relative to the other to increase a force of each contact tip (13C) against the corresponding contact pad (12) so as to flex the flex portion (13B) of each probe. The flex portion (13B) of each probe has a curvature such that the flexing causes the contact tip (13C) of that probe to rock without substantial sliding on the corresponding contact pad (12), the rocking and the needle force together cause lateral displacement of oxide from between the contact tips and the metal of the corresponding contact pad.